Will the Zenoah G-38 mount onto a plane which has a G-23 on it without having to drill new mountholes in the firewall? I can not find the dimensions of the G-23 bolt pattern. Thanks for any help.

Not even close...If the G23 is a new model with the aluminum backplate you could get a G26 (same bolt pattern) and get the same or more performance with less weight...
My tests show the G26 turning more rpm with a Mejzlik 18-6 than a G38 with the same prop....17 1/2 lbs pull on a spring scale...

Thanks for the info. Although you kinda lost me with the G-26 vs G-38. I would have thought the G-38 would be way more power. Again thanks!

G26 18-6 Mejzlik 8700 rpm
G38 18-6 Mejzlik 9000 rpm

The G26 will not turn 18-8 or 20 inch props as well as a G38...

An 18x6 prop on a G38 is seriously underpropping it. You are stressing the rpm capability of the engine and are well over the torque curve peak. Put an 18 x 10 on both and you will see a difference the other way. That is seriously overpropping the G26. Is apples and oranges.

However, the comment that you might want to consider the G26 is very valid. People say good things about them.

Gerry Rosebery

I have been working on and selling Zenoah engines for 16 years.. Here are the speeds quoted directly from the latest Zenoah owner manuals..
G26..Recommended prop sizes..18x6-10, 16x8-12..Max power, 1.62 @ 12,000..Max torque, 1.48 @ 9000 rpm..The max power for the 23 cc Heli engine is 1.58 @ 13,000..

"Be sure to use a propellor which makes the engine speed approximately 7000-8500rpm while the airplane is flying"

G38...Service engine speed 7000-9000 rpm..
Allowable engine speed (instantaneous) 12000 rpm..

Anyone out there smarter than the Zenoah engineers ?

B H Hanson turns the Small Zenoahs somewhere around 14,000 rpm in boats...
I can copy the Zenoah manual if anyone wants to actually READ it....
Not reading the instructions is the reason people buy the GT 80 twin and try to fly it turning a big prop at 6500 rpm..DUH....

Yes - Don't run a G38 at 9000 rpm or even near it. It won't thank you. Best rpm range from my experience with them is 7000-7800 on the ground (I don't often measure it in the air. I wonder how Zenoah does it?) The 18x6-10 is a good prop for the G38 but I have found that an 18x10 pulls better once they are run in.

Gerry Rosebery

Engine speed in the air can be measured either of 2 ways, an on board data logger or an audio tach that listens to the engine in the air.....On board data loggers show our Aerrow 200 twin race engines turning 10,000 plus in the air at 220+ mph............